1. Field of the Invention
The present invention relates to a Gigabit Ethernet passive optical network (GE-PON) and, more particularly, to an apparatus and method for transmitting data from optical network units (ONUs) to an optical line termination (OLT) in a GE-PON.
2. Description of the Related Art
FIG. 1 shows the configuration of a GE-PON being standardized in IEEE802.3ah EFM to which the present invention is applicable. As shown, a plurality of ONUs 110-1, 110-2 and 110-3 are configured to communicate with one OLT 100. During downstream transmission from the OLT 100 to the ONUs 110-1, 110-2 and 110-3, the OLT 100 broadcasts data to all the ONUs 110-1, 110-2 and 110-3, and each of the ONUs 110-1, 110-2 and 110-3 is configured to receive the intended data from the OLT 100. However, during upstream transmission from the ONUs 110-1, 110-2 and 110-3 to the OLT 100, the ONUs 110-1, 110-2 and 110-3 transmit a frame to the OLT 100 based on a time-division multiple access (TDMA) scheme.
Referring to FIG. 9, if a malfunction occurs in any one of the ONUs during the upstream transmission, the transmission times allocated to the other ONUs may be affected. As can be seen from this drawing, the ONU1 110-1 may succeed in transmitting an ONU1 data frame during a first period, and the ONU2 110-2 fails to transmit an ONU2 data frame within a second period due to the occurrence of an error therein, thereby continuously occupying the transmission line thereafter. As the ONU2 110-2 continuously transmits the erroneous ONU2 data for more than the predefined time, it causes a data collision in a third period, during which the ONU3 110-3 is permitted to transmit an ONU3 data frame. As a result, the entire transmission of the GE-PON will be disabled if such data collusion occurs continuously.